<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style type="text/css">
        .box {
            width: 300px;
            height: 300px;
            background: #eeeeee;
            margin-left: 20px;
            margin-right: 30px;
            margin-top: 40px;
            margin-bottom: 50px;
            /* 外边距连写 */
            margin: 20px 30px 40px 50px;
        }
    </style>
</head>

<body>
    <div class="box"></div>
</body>

</html>